Solar, or sunshine, sensors are used in vehicle ventilation systems to compensate for sunshine irradiated into a car onto occupants of the vehicle. Advanced ventilation systems currently provided for cars can be provided with a thermostat that can be set at a predetermined temperature, such as 72.degree. F. While the interior of the car can be controlled to maintain the predetermined temperature through heating or air conditioning, comfort is not assured unless there is a mechanism to compensate for the apparent increase in temperature caused by sunlight being directed upon the occupants when the sun is at a low azimuth angle. The vehicles ventilation system may be set to maintain a temperature of, for example, 68.degree. to 72.degree. F. However, with direct sunlight entering the vehicle at 9:00 in the morning when the vehicle is heating east, the occupant may be uncomfortable at that range of temperature unless the ventilation system can compensate for the sunlight by controlling the interior of the car to a cooler temperature by several degrees. The solar, or sunshine, sensor is used to provide information to the ventilation system control as to the direction and angle of sunlight entering the vehicle.
Various prior art approaches to this problem have produced complex and costly systems for providing this temperature compensation. For example, in U.S. Pat. No. 5,181,654, a system is disclosed wherein three diodes are provided on three differently angularly oriented surfaces whereby sunshine components including elevation angle, azimuth and heat reception quantity are measured. It was an object of that system to measure the elevation angle, azimuth angle of the sunshine and quantity of heat received by the car. These measurements are computed by matching the sum vector of the normal vectors of three light receiving elements. This is a complex and expensive system.
Another proposed solution to this problem is disclosed in an article entitled, Solar Sensors-Dual Zone, Uniform, and Fifty Percent Overhead Response. The solar sensor in this article includes a photo diode that is covered by a diffuser and a dark lens cover that absorbs light striking the diffuser when the sun is overhead by 50 percent of its maximum value. This solar sensor is relatively expensive and can provide inaccurate compensation if the sun is directed from the rear or side of the vehicle onto the sensor.
The above problems are addressed by the present invention in a cost-effective manner as summarized below.